It is known to use resistances to reduce overvoltages which may occur in very high tension grids when closing or re-closing a long line which has remained charged by interrupting the capacititive current.
The value of such a resistance must be close to that of the characteristic wave impedance of the line. However it is advantageous to be able to vary the duration of resistance insertion depending on the grid in question, and a circuit-breaker is more versatile if it can be adapted without great modification to shorter or longer insertion times.
To obtain this result, the resistances used are switched in and out in an auxiliary chamber controlled by operating units which are independent of, or at least adjustable with respect to, the unit which operates the main chamber of the circuit-breaker. However, this leads to bulky equipment which is more expensive and requires two chambers and two operating units.
If both the main chamber and the auxiliary chamber are placed in the same casing, this casing is very bulky.
In the case of a compressed gas operating unit, the delay of the main chamber can be adjusted relative to the auxiliary chamber by use of dead volumes and consequently the duration of insertion can also be adjusted. If the operating unit is mechanical, as is generally the case with auto-compression sulphur hexafluoride type circuit-breakers, it is necessary to have two operating units if the resistance is not to be in circuit at the time of release.
The invention aims to produce a compressed gas circuit breaker with a device for inserting a resistance only on closing there being only one operating unit and the circuit-breaker being compact.